TYPES OF VACCINES: DEAD OR LIVE?

TYPES OF VACCINES: DEAD OR LIVE?

Vaccines have traditionally come in two basic forms: dead (inactivated or killed) or live. The vast majority of both forms are delivered one of two ways: via injection under the skin (subcutaneous) or into the muscle (intramuscular). (Polio and typhoid vaccines are also available in oral form.) In some cases, both live and killed vaccines are available to treat the same disease.

A third type of vaccine, the recombinant DNA vaccine, is the product of genetic engineering. It is the newest form but there are remaining questions about safety and efficacy.

Live Vaccines

Live vaccines are made in a laboratory from the living organism (usually a virus) that causes the disease. Live vaccines are attenuated, or weakened, so they will cause the body's immune system to generate an immune response without (hopefully) causing the disease. Some people, however, do respond to a vaccination by developing symptoms of the disease, although in most cases they are mild. Examples of live attenuated virus include polio (oral), measles, mumps, chicken pox, rubella, and yellow fever. Live bacterial vaccines include one for typhoid fever and Bacillus-Calmette-Guerin (BCG) vaccine, which is used for tuberculosis.

Some experts claim that the immune system responds to live, attenuated vaccines the same way it does to a natural infection; others disagree. In fact, even proponents of live vaccines agree that live vaccines can cause a mild version of the disease they are designed to prevent. People who question the wisdom of giving live vaccines, especially to infants and young children, say these vaccines may have much more serious consequences, pointing to the correlation with autism and autoimmune diseases.

Killed Vaccines

A killed, or inactivated, vaccine consists of all or part of the disease-causing organism that has been killed or rendered inactive. Unlike live vaccines, killed vaccines cannot reproduce, so they are not able to cause the disease they are designed to prevent. They trigger a weaker response by the immune system than do live vaccines. They also tend to be safer than live vaccines for people who have a weakened immune system, for pregnant women, and for children younger than one year.

Most killed vaccines are protein-based, like the bacteria they mimic. Some of these bacteria are coated with sugars called polysaccharides. When scientists tried to develop vaccines for sugar-coated bacteria, they found that pure polysaccharide vaccines didn't work well in infants. But when they joined (conjugated) the polysaccharide to a protein, the vaccines were much more effective for infants and young children.

Inactivated vaccines are used for the following diseases: cholera, hepatitis A, hepatitis B, influenza, Lyme disease, plague, pertussis (whooping cough), polio (injected), rabies, and typhoid.

Another type of inactivated vaccine are toxoids, which are made by inactivating the toxins (poisons) produced by bacteria and viruses. The vaccines against diphtheria and tetanus are toxoids.

Recombinant DNA Vaccines

Another type of vaccine is a recombinant DNA (genetically engineered) vaccine. The hepatitis B vaccine is one example. Rather than using the entire organism, recombinant DNA vaccines are made by taking specific genes from the infectious agent (for example, virus, bacteria) and adding them to the vaccine culture. For example, hepatitis B vaccine is made by inserting a portion of the hepatitis B virus gene into baker's yeast, the culture in which this vaccine is produced.

Experts say recombinant DNA vaccines are more effective and safer than other types of vaccines because they don't contain the entire infectious agent and thus cannot cause an actual infection. However, the greatest concern about recombinant DNA vaccines is that they may cause the immune system to produce antibodies, which in turn attack parts of the body and cause health problems. Much is still not known about the effects of recombinant DNA vaccines.

(SOURCE: Stephanie Cave and Deborah Mitchell (2007). What Your Doctor May Not Tell You About Children's Vaccinations)